Placental blood contains a very high concentration of hematopoietic stem cells and other precursors. The numbers of stem cells are sufficient to repopulate bone marrow and sustain hematopoiesis when given to bone marrow-ablated, conditioned, HLA-identical siblings. It is proposed to determine whether placental blood may by cryopreserved and stored for use by HLA-matched unrelated recipients. Placental bloods will be harvested in hospitals serving two large metropolitan areas to ensure adequate proportions of donors of diverse ethnic groups. All placental blood units will be HLA-A,-B and -DR typed and will be comprehensively tested for transmissible infectious agents, as will blood samples of mothers who consent. Leukocyte counts and other hematological indices will be determined. The numbers of colony-forming cells, an index of stem cell activity, will be measured and all results will be included in a computerized database. The placental blood units will be cryopreserved and stored for use in transplantation and aliquots will be preserved for pre-transplant testing. Cryopreserved units will be used as a pool for the selection of compatible hematopoietic tissue for bone marrow restoration in patients who do not have HLA-identical or well-matched related donors in our own and in two collaborating institutions. The expected number of transplants will be sufficient for preliminary comparisons to the results of unrelated bone marrow grafts. Cryopreserved units will also be made available for use by other bone marrow transplantation services. The data to be generated will be used to estimate the clinical, technical and financial feasibility of establishing similar programs on a national scale.